Much has been done to reduce the fuel consumption of internal combustion engines. This generally can be achieved by making the combustion, that is the release of energy as efficient as possible. The design of the combustion chamber and the composition of gas is of great importance. Also, by reducing the internal losses in the form of flow and friction losses of the engine the efficiency can be substantially raised.
Flow losses in the form of gas exchange or pumping losses arise when combustion gases are going to be replaced by the engine by a new working medium after the working stroke. These losses are particularly obvious when the engine is controlled by a throttle and is operating in the low load and partial load range. The car engines of today are very much oversized to offer relaxed and restful driving with a large power in reserve for rapid acceleration. This implies that driving in the city and on the main, with other words the most common driving conditions, the engines are operating with large pumping losses.
At inlet of fresh gases to the cylinder of an internal combustion engine there is pressure drop because of the flow in the ducts and at the valves and the throttle. These pressure drops gives rise to a negative pressure in the inlet system. In the same way at exhaust of exhaust gases there is a positive pressure in the exhaust system because of the flow resistance. This pressure difference is the reason for work to be consumed to pump the gases into and out of the cylinders and this is called gas exchange work or pumping losses.
In the pV- diagram, see FIG. 1, the area between the inlet line and the exhaust line the pumping work. In the logarithmic pV-diagram, FIG. 1a, the pumping cycle is brought about and therefore this is used hereinafter. To compare, the real proportions are seen in the linear diagram, FIG. 1b.
The power of the auto engine is controlled by varying the inlet gas mass. Since the inlet volume all the time is constant, and equal to the cylinder volume of the engine, the density of the gas has to be varied. This is achieved by the gas being choked by a butterfly valve or a throttle. The control method per se thus implies that the pressure of the inlet gas has to be reduced in order to reduce the power. At full load the throttle is fully open and in that case very small pressure losses are obtained at the inlet. At low load however there is a very small throttle opening which gives a very great pressure loss because of the choking. Through the throttle control the engine thus has to work with a lower pressure than atmospheric pressure on the inlet side. When the piston is taking in air at a lower pressure a larger amount of work is consumed. The lower load on the engine the lower is the inlet pressure which makes the pumping losses increase. From FIG. 2 can be seen that the pumping losses increase considerably at low load. A comparison at constant speed shows that the pumping losses at full load may be about 5% of indicated power while they are about 50% at low load.
The engines of passenger cars of today are driven during the major part of the time at very low load, at the magnitude of 20% of the maximum power. At normal driving thus a very little throttle opening is used, which results in the pumping losses being largest in the operational range in which passenger cars are most often driven.
The method according to which the pumping losses are going to be reduced according to the present invention can be derivated from the equation of state: EQU pV=mRT implies p=mRT/V (1)
Here we let p be the inlet pressure in an arbitrary position of the inlet stroke The rest of the parameters are:
m=mass (air-fuel mixture) PA1 R=gas constant PA1 T=temperature of the mixture PA1 V=sA+Vc=volume PA1 s=stroke PA1 A=piston area PA1 Vc=compression volume PA1 * A decrease of V PA1 * An increase of m PA1 * An increase of T
All efforts to reduce the pumping losses at low load aim to increase p. Without affecting the maximum power of the motor from eq. (1) it can be achieved:
At low load the volume can be reduced by in some way reducing the stroke: either the geometric or the effective intake stroke. With the effective intake stroke is here meant the part of the stroke when intake occurs. Moreover the volume can be reduced by disengaging a number of cylinders of multiple cylinders at low load.
Methods in known technique which apply reducing of the effective intake stroke are available in two variants namely:
Early closing of the intake valve, EIVC (Early Intake Valve Closing), and late closing of the intake valve, LIVC (Late Valve Intake Closing). Devices according to these methods controls the engine power by continuously varying the closing time and lift of the intake valve.
With EIVC is meant that intake valve closes before lower dead point. In certain designs there is no throttle at all. A degree value after the designation of the control method states the time for valve closing in reference to the lower dead point.
E.g. EIVC 60: The valve closes 60 degrees before the lower dead point.
At load control using EIVC the intake valve opens as in a conventional engine just before the intake stroke. As the cylinder volume increases during the intake stroke the fuel-air mixture is let in at nearly atmospherical pressure, since no choking butterfly valve is present.
Thereafter the power is controlled by closing the valve when a sufficient amount of mass has flowed in. With other words the power is controlled by the time for valve closing. After the closing the gas expands simultaneously as the piston completes the intake stroke. Thereafter compression, expansion and exhaust follows as in a conventional engine.